I’d guess the general interest in a C-based IF system would be pretty low.
From time to time, IF enthusiasts come to the table with alternate IF authoring systems in which authors can develop IF in a “real” programming language, typically one of the top 20 languages on the TIOBE index or at least a language that ranks highly on StackOverflow’s “most loved languages” list. insights.stackoverflow.com/surv … and-wanted
But none of the most popular IF systems require authors to use a “real” programming language. Instead, since most IF authors see themselves as writers first and coders second (if at all), all of the most popular systems use a domain-specific language for IF, ideally one that makes it easy to write extensions in another “real” programming language (typically JavaScript).
For comparison, Undum github.com/sequitur/raconteur
According to the StackOverflow survey, C is a language more dreaded than loved. Many people who can develop working programs in higher-level languages like JS or Python fail to accomplish anything at all in C. I would not expect a C-based IF system to be a big hit.
Having said that, if this scratches an itch for you, it could succeed anyway, if you’re prepared to do a lot of work on it.
Overall, the language that an IF system uses is arguably the least important factor in making it popular. The most important factor is to implement an entire complete “admirable” game. Most people decide to use an IF system because they see a game that they admire, and they say, “I want to make a game just like that! Whatever system the author used to make it, I’ll use that system, too!” Admirers don’t seem to directly care about any of the details of the system, except that if it’s too hard for them to learn the system and finish a game, that’s a major factor in achieving true popularity.
If you build an IF system that helps you to develop an admirable game for the Commodore 64, and you demo it on real C64 hardware (and maybe a few other legacy platforms) at expos, and then also make your game available on other more, ah, accessible platforms, you might be able to parlay your C64 compatibility into some attention in the press, which could develop into a real movement over time.
But if you’re asking: “if I just build a C-based IF system, will lots of great IF authors get excited about it and build great games in it?” I think history shows that the answer is no.